Accompanying the increasingly higher levels of integration of semiconductor devices in the semiconductor industry in recent years, there is a need for fine patterns that exceed the transfer limitations of conventional photolithography methods using ultraviolet light. Extreme ultraviolet (EUV) lithography is considered to be promising as an exposure technology that uses EUV light to enable the formation of such fine patterns. Here, EUV light refers to light in the wavelength band of the soft X-ray region or vacuum ultraviolet region, and more specifically, light having a wavelength of about 0.2 nm to 100 nm. Reflective masks have been proposed as transfer masks for use in this EUV lithography. Such reflective masks have a multilayer reflective film that reflects exposure light formed on a substrate, and an absorber film that absorbs exposure light formed in the form a pattern on the multilayer reflective film.
The reflective mask is fabricated from a reflective mask blank having a substrate, a multilayer reflective film formed on the substrate, and an absorber film formed on the multilayer reflective film, by forming an absorber film pattern by photolithography and the like.
Deposition of a multilayer film and absorption layer is formed by a deposition method such as sputtering. During this deposition, the reflective mask blank substrate is supported within a deposition device by a support means. An electrostatic chuck is used for the substrate support means. Consequently, in order to proceed immobilization of the substrate by the electrostatic chuck, an electrically conductive film (a back side electrically conductive film) is formed on the back side of a glass substrate or other insulated reflective mask blank substrate (side on the opposite side from the surface having a multilayer reflective film and the like formed thereon).
Patent Literature 1 describes an example of a substrate with an electrically conductive film that is used to fabricate reflective masks for EUV lithograph, wherein the electrically conductive film is characterized in that it contains chromium (Cr) and nitrogen (N), the average concentration of N in the electrically conductive film is 1 at % to less than 40 at %, crystalline state of at least the front side of the electrically conductive film is amorphous, the surface roughness (Rms) of the electrically conductive film is 0.5 nm or less, and the electrically conductive composition employs a graded composition in which the concentration of N in the electrically conductive film changes in the direction of thickness of the electrically conductive film so that the N concentration is lower on the substrate side and is higher on the surface side.
Patent Literature 2 describes a substrate with an electrically conductive film used in the fabrication of reflective mask blanks for EUV lithography, wherein the main material of this electrically conductive film is at least one material selected from the group consisting of Cr, Ti, Zr, Nb, Ni and V, the electrically conductive film contains B (boron) at an average concentration of 1 at % to 70 at %, and the electrically conductive film employs a graded composition in which the concentration of B in the electrically conductive film changes moving in the direction of thickness of the electrically conductive film so that the average concentration of B is lower on the substrate side and the average concentration of B is higher on the surface side.
Patent Literature 3 describes a friction coefficient measuring apparatus comprising a frictional force generation means and a compression load generation means for generating a compression load.